1. Field of the Invention
The present invention relates in general to a method and an apparatus for machining, grinding, plastic working and other physical working operations performed on a workpiece, and more particularly to a technique relating to the use or application of a cutting or working liquid in such working method and apparatus.
2. Discussion of the Prior Art
An operation to physically process a workpiece by a working tool is effected with or without application of a working liquid such as a cutting liquid or coolant to a working area of the workpiece and tool. An operation without using the working liquid is sometimes called "dry" working, which is employed, for example, when the workpiece is ground, or when a brittle material such as a cast iron is machined. In this case, the cutting chips produced may be scattered around the working apparatus or machine, and the working environments are deteriorated.
An operation using the working liquid is sometimes called "wet" working, which is performed while the working liquid is applied to the working area which includes the point of contact between the working tool and the workpiece. The working liquid may be an oil, or an aqueous solution or suspension of a coolant and/or a lubricant. The function of the working liquid is to prevent scattering of the cutting chips produced during cutting, grinding or other working operation, to cool the working tool and workpiece which are heated by friction, and to lubricate the tool and workpiece for lowering the frictional resistance.
The conventional "wet" working method and apparatus suffer from several drawbacks as described below.
First, the working liquid which usually flows through the working area should be continuously fed throughout a working operation. Further, a large volume of the working liquid is necessary to prevent the scattering of the cutting chips, particularly for a grinding operation, or a machining operation on a brittle material such as a cast iron. This requires a large sized device for delivering the working fluid, and accordingly increases the working cost.
On the other hand, the working liquid or coolant has a larger cooling capacity than the ambient air, and may cause a sudden drop of the operating temperature of the working tool. As a result, the working tool undergoes temperature changes due to the heating by friction and the cooling by the working liquid, and is therefore susceptible to thermal cracking or damage, which may deteriorate the working accuracy, and shorten the service life of the working tool.
Where the wet working operation such as a form rolling, broaching or tapping operation requires the use of a comparatively expensive working liquid such as an oil, or an aqueous working liquid having a high concentration, the consumption of the working liquid results in a significant increase in the working cost. The working liquid is consumed because it is transferred to the machined or otherwise processed workpiece, and may be disposed of with the cutting chips.